Charged me double and wont refund me!

I was forced to buy 2 items with a buy one get one free promo (there was not option to only take one as it was a special....

The amount in my cart showed the charge for one but they charged my card double (the the price for 2) and now won't refund me. Apparently I have to try the promo code again & hopefully this time it wont charge me... ***???